Acquisition Processing for the TDRSS Simulator

Abstract

The TDRSS simulator forward link acquisition process requires that the epoch and frequency of the spreading code be acquired, and that the incoming carrier be phase locked. The time required for these two acquisitions must meet a specification of 20 seconds for S band and 4 seconds for K band operation. Calculations for the time required to acquire the carrier show that with the allowable sweep rates and frequency uncertainties the acquisition time specifications cannot be met with conventional sweep lock circuitry. Parallel processing is possible, but the requirements on local frequency control become difficult, and the additional circuits required make this approach unattractive. Because of these considerations, a frequency control strategy was developed which reduces the carrier acquisition time to fractions of a second. The specified acquisition time can then be allotted almost entirely to the spreading code acquisition process. This strategy is described in detail, including an experimental verification of the technique. The technique has an additional advantage of eliminating false lock to data sidebands in the carrier loop.